It is common practice to use a scintillator in combination with an image sensor to capture x-ray images. In such a setup, the scintillator absorbs x-ray photons and emits secondary photons, which are typically in the visible part of the electromagnetic spectrum and can be detected by an image sensor placed behind the scintillator. In an unstructured or semi-structured scintillator, the secondary photons spread laterally while traveling through the scintillator towards the image sensor. This results in blurring of the image because the image sensor registers signal not only in the pixel right below where the x-ray photon was absorbed, but also in other pixels in its vicinity. This mechanism deteriorates the image resolution of the x-ray detecting system and in many cases limits the achievable image resolution of the system. To overcome this problem, a structured scintillator comprising a micromechanical structure such as a pore matrix filled with scintillating material can be used. The structured scintillator eliminates, or at least significantly reduces, the lateral spread of secondary photons in the scintillator, thus avoiding deterioration of the image resolution.
In some applications, the use of micromechanical trenches, functioning as elongated scintillation strips is of particular interest, for example as scintillating gratings in x-ray phase contrast imaging.
When melting and solidifying scintillator material in micromechanical structures, there are many factors that determine the quality of the final crystal. In a conventional furnace, there is often problem with formation of bubbles during the melting, leading to undesired voids in the solidified scintillating material. Another problem with a conventional furnace is that heating is typically more or less isotropic, which means that there is little or no control of the nucleation process, i.e. of where nucleation starts during the solidification process. In addition to the undesired formation of voids mentioned above, this uncontrolled nucleation also typically results in an undesired poly-crystalline structure with small crystal grains, rather than the desired large crystal grains or ultimately single-crystalline structure. Due to these effects, there will typically be non-uniform characteristics when measured over the area of the scintillator, in terms of (i) x-ray absorption, (ii) efficiency of secondary photon generation, and/or (iii) optical guiding of the secondary photons towards the exit surface of the scintillator.